In Plain Sight is a law-enforcement drama with a twist: It deals with the innocent as well as the guilty.

The new USA Network series (Sunday, 10 ET/PT), off to a solid ratings start (averaging 4.6 million viewers after three episodes), focuses on the federal witness-protection program, which creates new identities for those endangered because of testimony in criminal cases.

U.S. Marshals run the program, moving both criminals and those who may have witnessed a crime and are needed to obtain a conviction.

McCormack (The West Wing, Private Parts) says the varying situations allow for an array of witnesses, from a Mob killer to an affluent family in which a daughter witnessed a gang shooting. Sunday's episode features an ambush as the Marshals transport an annoying man (Dave Foley) who works as a go-between for a hit woman.

"Some of the stories are mysteries. Some of them are much more emotional. Week to week, the tone is going to shift in terms of what the story involves," she says.

McCormack says her character, intense and gruff, was a good fit. "I rant a little bit. I'm definitely a bit grouchy, definitely quick to judge," she says. "I'm not into anything mystical or magical. I'm organized."

Executive producer David Maples wrote the pilot without McCormack in mind but found the parallels between her and Shannon "bizarre." Both are Irish Catholics from New Jersey named Mary. In an even odder connection, Shannon's nickname for her sister (Nichole Hiltz) is Squish, as is McCormack's for her elder daughter.

But Maples' main reason for casting her was she embodied the character: "beautiful and funny and warm and tough."

McCormack appreciates the opportunity to play a rough-edged lead character whose messed-up personal life contrasts with her successful career. Her mother (Lesley Anne Warren) and sister are constant headaches, and she resists emotional intimacy with a sometimes boyfriend (Cristián de la Fuente). "It used to be the boy role, the one who breaks the rules and gets the gun," she says.

Sight is part of a trend of programs that feature capable but quirky law women, including TNT's The Closer and Saving Grace. Maples bristled against reviews that referred to the show as a Johnny-come-lately to the genre because he wrote the pilot in 2004, before the others were on TV.

"But the reality is, it shouldn't really matter. The show either works and holds an audience, or it doesn't," he says.

Maples, who consulted with U.S. Marshals with experience in witness protection, says he enjoys writing roles for women. "We had the opportunity to sit down with a female WitSec (Witness Security) inspector. … There were a lot of similarities (with) Mary. After she watched the pilot, she said, 'When this comes on the air, my family is going to think it's about me.' "

Maples and McCormack say the show hit its stride as it filmed more episodes, finding a good dramatic tone after a pilot that he says was "more intentionally comedic."

Sight fits in with other USA series, including Monk, Psych and Burn Notice, but distinguishes itself by focusing on the witness-protection program and putting a woman on the case, USA president Bonnie Hammer says. "Tony Shalhoub and Monk set the template and focal point for where all our series should start: aspirational, blue skies to some degree, drama with a significant twist of humor," she says. "They can be as light as Psych… or, as in In Plain Sight, a little heavier drama."

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In the line of duty: Mary Shannon (Mary McCormack) tries to help partner Marshall Mann (Frederick Weller).

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